While there have been significant advances in the methods employed for the loading and unloading of vessels, the loading of refrigerated, cartonized cargo, and in particular, frozen animal products has proved particularly difficult due to several intractable problems. As a result, the transfer of the products from the packers to their loading aboard a vessel is presently carried out by processes that involve high costs and significant expenditure of manual labor, and which include bottlenecks that slow the process, that may result in product degradation or spoilage, and that result in long loading times for the product onto the vessel. It is presently common for the handling of cartons of frozen animal products to proceed as follows.
A large volume of animal products such as frozen chicken, turkey, beef, pork and seafood products (including livers, hearts, parts, deboned meat and the like) are frozen and shipped in and from the U.S. in relatively flat boxes. For example, chicken thighs, legs or quarters may be shipped in cartons of about 23.5 inches in length by 16.5 inches in width by 4 to 6.25 inches in height (59.7 cm by 41.9 cm by 10.2 to 15.9 cm). A preferred standardized box size for use with this invention, however, would be 24 inches by 16 inches (61.0 cm by 40.6 cm) with the height of the box varied to hold the particular products to be shipped. A box of such chicken parts may weigh on the order of 35 to 45 pounds (16 to 20 kg).
For simplicity, reference will hereafter be made to cartons of chicken parts, as other animal products may be handled in a similar manner.
Owing to the size restrictions imposed by standard trucks and trailers, the cartons are normally stacked on 40.times.48 inch (102.times.122 cm) pallets in layers of five cartons arranged with two cartons placed on the pallet in an end-to-end relationship beside three cartons placed side to side with their long axes perpendicular to those of the first two cartons. A palletload of cartons generally contains between about 10 to 12 such layers of cartons.
The packer sends the fresh chicken parts in such palletloads to a blast freezer/cold storage warehouse. At the warehouse, the cartons are restacked with spacers between the layers thereof. The spacers allow the circulation of air between the layers of cartons. Once the cartons are so stacked, the palletload of cartons are transferred to a blast freezer, which forces air chilled to about -40.degree. F. (-40.degree. C.) between and around the cartons. When the freezing process is completed, the cartons are removed from the blast freezer and placed in a rotator. The load of cartons is then rotated 90 degrees onto its side, the spacers are removed, and the load of cartons is then rotated back to an upright position in which it rests once more on the pallet. In order to facilitate transportation and storage of the stacks of cartons, the stack may be wrapped with a stretchable plastic film to help prevent excessive sliding of the layers of cartons relative to one another. Lift trucks are then used to move the cartons of frozen chicken products and transport them into the cold storage warehouse.
When the time comes to load a ship, lift trucks are used to remove the palletloads of cartons of chicken parts from the warehouse, and the cartons are placed inside dry van trucks or truck trailers for transportation to the dock. These are typically uninsulated and unrefrigerated, and thus can be deleterious to the frozen product contained therein. At the dock, the cartons are removed from the truck trailer and placed on the dock, where they are subsequently lifted into the hold using the ship's gear, such as by using slings, lifting platforms or flying forks to lift the cartons and pallets.
In the hold, lift trucks engage the pallets and transport the pallets with their stacks of cartons to locations near where the cartons will be stowed. Stevedores then manually remove the cartons from the pallets and stack them without pallets for shipping. The pallets are then returned to the square of the hatch and are stacked to be hoisted out of the hold and back onto the dock by the ship's gear. The square of the hatch is the volume of space extending vertically downward from the open hatch to the floor of the cargo hold.
This process is quite inefficient. Delays in bringing a sufficient quantity of product to the dock and in unloading the cartons from the truck can increase the time needed to load the vessel. The space constrictions in the vessel limit the number of workers who can be engaged in stowing of the cartons, and thus may create a backup for product arriving at the dock. Excessive delays in loading which result in the cartons being left on the dock or in the truck can allow the product to begin to thaw, which can result in spoilage or otherwise render the product unmarketable. Delay in loading may also result in increased condensation of moisture on the cartons which can complicate the handling process. As the industry is seeking to use less wax on the cartons and to utilize paper-coated boxes, the damaging effect of condensation and internal thawing on the boxes is increased.
The breakage rate for pallets during this process is fairly high. As many as half of the pallets may suffer some breakage, and this can result in splintered wood, which may contain protruding nails, being left at the warehouse, on the dock or in the cargo hold of the vessel. Additional work is thus required to collect the pallets and pallet debris, to extract it from the hold of the ship or remove it from the dock, and to repair or discard the broken pallets. Further, the existence of pallet debris at the warehouse, on the dock, and in particular in the hold of the vessel, presents a risk of injury to workers.
Inefficient as this method of handling may be, there are a number of constraints that have made it difficult to improve. The main problems encountered is that the holds of the ship are irregular both in the overhead clearance and in the shape of the floor space. Not only does the overhead clearance of the cargo holds vary from ship to ship, and perhaps within a ship from hold to hold, the internal structure of the vessel and of the cooling system within it can result in overhead clearances that vary depending on the location within the hold.
Another difficulty in loading such cargoes is that the cartons are typically stacked to a uniform height after freezing. This is necessary for efficient use of the cold storage warehouse. This uniform height is generally ten or twelve layers of boxes arranged on a lift truck pallet, but it may vary somewhat from this number depending on the size of the cartons. The cartons are unitized by wrapping them with a stretchable plastic film that aids in transportation of the palletloads by fork lift, etc. However, space on refrigerated vessels is at such a premium that the wasted space of such pallets is considered undesirable. Thus, it has been considered necessary to avoid stowing the cartons on the pallets, and thus it has been the practice to stow the cartons in the ship by restacking them without the pallets within the ship. Moreover, since the ceiling height of holds on ships varies, and is seldom equal to the height of the cartons when stacked for warehousing purposes, it has heretofore been considered essential to manually stack the cartons in order to obtain as complete a filling of the vessel as possible.